G57: Ordering the content in a meaningful sequence

Important Information about Techniques

See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.0 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0.

Applicability

Description

The objective of this technique is to ensure that the order of content presented to assistive technologies allows the user to make sense of the content. Some techniques permit the content to be rendered visually in a meaningful sequence even if this is different from the order in which the content is encoded in the underlying source file.

For example, when mixing languages with different directionality in HTML, the bidirectional algorithm may position punctuation in the wrong location in the visual rendering. The visual rendering problem could be corrected by moving the punctuation in the content stream so that the bidirectional algorithm positions it as desired, but this would expose the incorrect content order to assistive technology. The content is both rendered in the correct order visually and exposed to assistive technology in the correct order by using markup to override the bidirectional algorithm.

When rendered visually, white space characters such as space or tab may not appear to be part of the content. However, when inserted into the content to control visual formatting, they may interfere with the meaning of the content.

At a larger granularity, controlling the placement of blocks of content in an HTML document using layout tables may produce a rendering in which related information is positioned together visually, but separated in the content stream. Since layout tables are read row by row, if the caption of an illustration is placed in the row following the illustration, it may be impossible to associate the caption with the image.

Examples

Example 1

A Web page from a museum exhibition contains a navigation bar containing a long list of links. The page also contains an image of one of the pictures from the exhibition, a heading for the picture, and a detailed description of the picture. The links in the navigation bar form a meaningful sequence. The heading, image, and text of the description also form a meaningful sequence. CSS is used to position the elements on the page.

Tests

Procedure

Linearize content using a standard approach for the technology (e.g., removing layout styles or running a linearization tool)

Check to see if the order of content yields the same meaning as the original

Expected Results

Check #2 is true.

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.